Fluid shock absorber struts which are used in a vehicle suspension system often experience a bending moment caused by the offset of the tire contact patch with the roadway from the strut centerline. This offset loading increases the sliding friction between the piston rod and surrounding cylinder, increasing harshness and reducing the life of the shock absorber strut. One of the most commonly used means to counteract this offset loading on a fluid shock absorber strut such as a McPherson strut, is by the use of a system wherein a counter lateral force is exerted on the strut by the use of an offset or angled coil spring surrounding the piston rod and cylinder.
Some examples of prior art suspension systems which attempt to overcome this offset loading problem are shown in the following patents.
U.S. Pat. No. 3,954,257 discloses a suspension system in which the extended end of the piston rod is connected to the underside of an upper spring and bearing assembly positioned within a suitable bracket connecting the suspension system to the vehicle. This suspension unit includes a surrounding helical spring and a rolling flexible diaphragm member connected to a periphery of a housing in which a fluid shock absorber cartridge is mounted with the upper end of the flexible diaphragm being connected to a spring retaining ring.
U.S. Reissue Pat. No. 31,184 discloses another suspension system which attempts to reduce this offset loading problem by the use of an elastomeric mounting arrangement at the extended end of the piston rod in combination with a surrounding coil spring. German patent No. 2,100,338 discloses another suspension system in which the piston rod of a fluid shock absorber is set at an offset angle to match the suspension system in order to counteract the heretofore unbalanced forces exerted hereon.
Another type of vehicle suspension system uses pneumatic springs commonly referred to as air springs in place of fluid shock absorber. In these air springs one or more pistons act within a chamber filled with a pressurized fluid or gas causing compression and expansion of the fluid contained in the pressure chamber, to absorb the road shocks as the pistons move between jounce and rebound positions. Some examples of prior art vehicle air springs are shown in U.S. Pat. Nos. 2,926,011; 2,985,445; 2,978,256; 3,046,000; 3,074,079; and 4,518,154.
Therefore, the need exists for a suspension system using a fluid shock absorber strut in combination with means for offsetting the off center lateral forces exerted on the shock absorber strut. There is no known suspension system of which we are aware which accomplishes this by the combination shock absorber strut/air spring suspension system in which the air spring is provided with means of exerting an offset loading to counteract the bending moment caused by the unbalanced load exerted on the shock absorber strut and without interfering with the tire when in the jounce position.